Exsultet

Borrowed from Latin exsultet (“let it [i.e., the angelic host] rejoice”), the first word of the prayer in the Roman Rite.

the Exsultet

1. (Western Christianity) A long prayer traditionally pronounced or sung at the Easter Vigil, beginning “Rejoice!” or “Exult!” in English.
   • 1997, Diana Kodner, Handbook for Cantors, 2nd edition, →ISBN, page 77:

     The Exsultet is the preeminent chant of cantor repertoire, both because of its difficulty and because of its importance in the liturgical year. Yet very few cantors have ever sung the Exsultet, or have seen printed music for it.